The present invention relates to a pressure reducer for internal combustion engines fed with liquid petroleum gasses; the reducer essentially comprises a valve for intercepting the liquid petroleum gas flow, a heat exchanger consisting of a first section in which the liquid gas is heated by means of the heat of the engine cooling water and a second section for heating the liquid gas with electrical resistors, an evaporation chamber, a device for regulating the gas pressure, an electronic central for controlling said pressure, gas absolute pressure sensors located at the outlet of the device for regulating the gas pressure, pressure sensors in the intake manifold of the engine and gas temperature sensors.